Embodiments of the invention relate generally to a switching system for switching a current to a selectable current path, and more particularly to micro-electromechanical system based switching devices.
A circuit breaker is an electrical device designed to protect electrical equipment from damage caused by faults in the circuit. Traditionally, most conventional circuit breakers include bulky electromechanical switches. Unfortunately, these conventional circuit breakers are large in size thereby necessitating use of a large force to activate the switching mechanism. Additionally, the switches of these circuit breakers generally operate at relatively slow speeds. Furthermore, these circuit breakers are disadvantageously complex to build and thus expensive to fabricate. In addition, when contacts of the switching mechanism in conventional circuit breakers are physically separated, an arc is typically formed therebetween which continues to carry current until the current in the circuit ceases. Moreover, energy associated with the arc may seriously damage the contacts and/or present a burn hazard to personnel.
As an alternative to slow electromechanical switches, relatively fast solid-state switches have been employed in high speed switching applications. As will be appreciated, these solid-state switches switch between a conducting state and a non-conducting state through controlled application of a voltage or bias. For example, by reverse biasing a solid-state switch, the switch may be transitioned into a non-conducting state. However, since solid-state switches do not create a physical gap between contacts when they are switched into a non-conducting state, they experience leakage current. Furthermore, due to internal resistances, when solid-state switches operate in a conducting state, they experience a voltage drop. Both the voltage drop and leakage current contribute to the generation of excess heat under normal operating circumstances, which may be detrimental to switch performance and life. Moreover, due at least in part to the inherent leakage current associated with solid-state switches, their use in circuit breaker applications is not possible.
U.S. patent application Ser. No. 11/314,336 filed on Dec. 20, 2005, which is incorporated by reference in its entirety herein, describes micro-electromechanical system (MEMS) based switching devices including circuitry and techniques adapted to suppress arc formation between contacts of the micro-electromechanical system switch.
The switching devices may be part of a current limiting protection device that may have to absorb or withstand a surge current associated with starting up a motor or other industrial equipment. This surge current often comprises multiple times (e.g., six times or more) the value of the steady state load current and can last up to ten seconds. One known technique of handling this current is to combine a number of MEMS switches (e.g., six times the number of switches required for handling the steady state current) in parallel. This technique perhaps will become cost-effective at some point in the future as the cost and yield of MEMS switch arrays improve, but presently to use six times the number of MEMS switches would increase the cost by six times, and these additional MEMS switches would only function for just about 10 seconds of operation. Accordingly, it is desirable to provide circuitry and/or techniques that reliably and cost-effectively handle such a surge current while still able to use the MEMS switches for the steady state operation and for addressing fault conditions that may arise.